1. Technical Field
The present invention relates to wireless communications and, more particularly, to conducting packet-data-communication sessions at least in part over a wireless link.
2. Description of Related Art
More people than ever are using mobile stations, such as cellular telephones and personal digital assistants (PDAs), to connect to wireless networks, which are also referred to as cellular networks, cellular wireless networks, wireless wide area networks, cellular wireless communication systems, and by other names. Wireless networks typically provide both voice and packet-data communication using a wireless communication format such as Code Division Multiple Access (CDMA), or another format.
To engage in packet-data communication sessions, a mobile station may first acquire radio-frequency (RF) connectivity by communicating with entities known as a base transceiver station (BTS) and a base station controller (BSC). The mobile station may then request packet-data connectivity by sending an origination request over a common air interface channel (such as an access channel) via the BTS and BSC to an entity known as a mobile switching center (MSC). The mobile station may include in the request a code that indicates a desire to establish a packet-data connection. In response, the MSC may then send the request to the BSC, which may include a functional entity known as a packet control function (PCF).
The BSC may then establish a radio link with the mobile station by directing the mobile station to operate on a particular traffic channel. Additionally, the BSC may signal to an entity known as a packet data serving node (PDSN). The PDSN and the mobile station may then negotiate in part over the radio link to establish a data-link-layer connection (“data link”), which may be a point-to-point protocol (PPP) connection. Packet data may then be exchanged over the data link between the mobile station and the PDSN (using the radio link, among other media), which then provides the mobile station access to a packet-switched network.
The mobile station, now communicatively coupled to the packet-switched network, is typically identified by a network address, such as an IP address, which may be dynamically assigned using either a Simple-IP or Mobile-IP process. In a Simple-IP process, the PDSN assigns an IP address to the mobile station once the data link is established. In a Mobile-IP process, the PDSN may transmit a registration request to a home agent associated with the mobile station. If the home agent approves the request, it may assign an IP address to the mobile station. Or the mobile station may use a permanently-assigned IP address.
Once the mobile station has an IP address, it may engage in packet-data communication via the PDSN with devices communicatively connected with the packet-switched network. This communication typically involves both sending and receiving IP packets. Other entities on the network are able to transmit packets to the mobile station by sending them to the mobile station's IP address. The packets are directed, perhaps via a Mobile-IP home agent, to the PDSN, which delivers the data to the mobile station via the data link (over the radio link, among other media).
Some mobile stations may be programmed to, upon registering with the wireless network, attain packet-data connectivity in the manner described above. That is, the mobile station obtains a radio link, a data link with a PDSN, and an IP address on the network. The mobile station may then enter what is known as a “dormant” mode, in which it releases its radio link but it and the network maintain the data link and IP address. That way, if the mobile station receives data addressed to the IP address, the mobile station can be paged to establish a radio link, and then the data can be forwarded to the mobile station over the data link and radio link.
However, from time to time, the PDSN may inadvertently drop the data link that had been established between it and the mobile station. That is, the PDSN may incorrectly cease to maintain connection data pertaining to the data link. This may occur if a particular timer value takes on a zero value, if a release command or message is mistakenly sent to the PDSN that causes the PDSN to delete the connection data pertaining to the data link, or for another reason.
If this inadvertent dropping of the data link by the PDSN occurs, the mobile station still operates under the assumption that the wireless network is maintaining both an IP address and a data link for it; that is, the mobile station operates under the assumption that it is reachable by other entities at its IP address. If other entities transmit packet data to the mobile station's IP address, that data will be routed to the PDSN. The PDSN will then determine that it has no data link with that mobile station, and will drop the data. The transmitting entity may eventually determine that it—or another device on the communication path, or both—has not received confirmation of delivery of the data. In the context of real-time media sessions, such as push-to-talk (PTT) sessions, this may result in a negative experience for a calling party, who may be prompted to start talking as if the session was starting properly, only to be notified after 10 or 15 seconds that the call had never in fact been established.
This problem may be somewhat ameliorated by the fact that the mobile station may be programmed to establish a new data link every so often. However, “every so often” may be as infrequently as once every ninety minutes. Thus, the mobile station may operate as if it is able to receive packet data—though in fact it is not—for whatever portion of that ninety-minute period remains following the inadvertent dropping of the data link by the PDSN. Note that a mobile station would also establish a new data link if, at any time during this period, it initiated a packet-data communication session of its own. But it may not.